1. Field of the Invention
The invention relates in general to dual mode system, and in particular, to a dual-mode communication apparatus capable of power management and a method thereof.
2. Description of the Related Art
In an embedded system, a real-time operation system (RTOS) has a timer management mechanism which provides a scheduling flexibility to every task based on an unique system timer. The tick source of this unique system timer may comprise an individual timer or several timers to generate interrupt signals on a regular basis at fixed time intervals that are short enough for the execution of real-time processing. In an embedded system for a communication application of a 2G or 3G system, the unit of the fixed time interval for the system timers is provided by a hardware timer's timing on the basis of a 2G-frame (4.615 ms) or a 3G-slot (0.667 ms), generating an OS tick at each fixed time interval.
Because low power performance is an important issue for a mobile communication system, a “power saving mode” is typically incorporated to reduce power usage in the system. Taking a 2G system as an example, the 2G clock is turned off during the power saving mode, consequently the OS tick is suspended and all system timers are withheld. When the 2G clock wakes up from the sleep mode, a sleep mode manager (SMM) informs the OS regarding the number of OS ticks that were skipped, so that the OS can update correct timing for each system timer accordingly, and restore the OS tick mechanism based on the 2G-frame.
In a dual-mode communication system where two communication systems, for example, a 2G and 3G system, operate on one communication apparatus, the OS tick is typically provided by only one communication system, for example, the 2G system. Since the two communication systems operate and enter the power saving mode by different timing, when the 3G system requires real-time OS service, the 2G system has to be waken up to provide the OS tick required for the real-time OS service request, resulting in complex clock control and increased power consumption.
Therefore, there exists a need to provide a dual-mode communication apparatus and a method for efficiently generating an OS tick for a real-time operation system in a dual-mode communication system.